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topic 43248

Two-step black color anodizing w/tin sulfate



A discussion started in 1998 but continuing through 2020

1998

Q. I do LASER engraving on anodized aluminum for botanical plates that are used outside. My supplier says that this material is for exterior use. However, after a few years the color on the plates seems to fade, especially on the ones facing south. I would appreciate your thoughts. Could this be UV rays causing the problem, and is this normal for anodized aluminum? I've sent a sample to my supplier for evaluation.

Thank you,

Bill Kramer
LECOR Enterprises, Inc.


TUTORIAL FOR NEWBIES:

Although anodized aluminum can be left natural color (the color of aluminum), it is very common to dye/color it. When aluminum is anodized, the anodized coating contains millions of tiny "drill hole" pores extending from the surface almost to the raw aluminum. The most common way to color or dye aluminum is to put this freshly anodized aluminum into a tank of dye, absorbing the dye into the drill holes, and then "seal" it with boiling water or other processes which hydrate/swell the aluminum to close off the pores.

Although some dyes are more stable than others, all organic dyes are subject to fading. So, for architectural anodizing intended for outdoor use, it is common to color the metal (usually in champagne to bronze colors or black) by filling those pores with metal-based coloring via processes called integral color anodizing or two-step anodizing.

Yet another variation is "overdying", where an inorganic dye is applied by two-step anodizing, then an organic dye is employed before sealing, in an attempt to give both a freedom from fading and a wider color choice.

1998

A. Sir,

Every anodize dye has a different lightfastness rating, meaning how well it hold up to outdoor light. Some dyes are not suitable at all for outdoor use.

Also, a poor seal could cause color fading.

David A. Kraft
- Long Island City, New York


1998

A. Bill,

You may want to look into electrolytic or the 2-step color anodizing. Light fastness is excellent.

Paul Davis



1998

A. Anodizers specializing in architectural applications will be most likely able to help you. They will need a 2-step (anodize then inorganic dye) process. The organic dyes just don't last as long in UV light.

F.A. Sandy Donaldson
- Minneapolis, Minnesota


1065
TALAT Lecture 5203: Anodizing of Aluminium
1998

A. Colors can only come from two sources; chromophores in organic chemicals that results from double bonds or triple bonds or a few other special bonds; in inorganics they come from metal ion complexes. UV light adds sufficient energy to break double or triple bonds so organic dyes are more susceptible to sunlight degradation. Try the inorganic metal dyes for outside use.

Dave Fairbourn
- Sandy, Utah


2000

Q. Accelerated test of light fastness of colored anodized aluminium seems to be made by ISO 2135 [affil. link to spec at Techstreet]

The Blue scale for evaluation is not easy to find anywhere and it is different from that one used for textile light fastness Could somebody tell me where can I find this special Blue scale to make this ISO 2135 test?

Many thanks G.Rizzotti

Gianmarco Rizzotti
- Busto Arsizio -Italy



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



1998

Q. DC/AC equipment for colour anodizing? I am looking for information on how to specify ripple, control, etc.to get the best choice for electro coloring anodizing in tin sulfate solutions.

Thank you, very much.

Gustavo C. Giraudo
Argentina


1998

A. I think such specifications are confidential information of manufacturers of AC/DC equipment who have spent a lot of money to develop them..

The best way to have such equipment is to contact with the AC/DC power suppliers' manufacturers and buy a suitable one.

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey


1998

A. I slightly and respectfully disagree with Mr. Ulucak just a bit, because there are some people who feel that complicated and expensive proprietary waveforms are a waste of money in tin-based electrocoloring, and that all that is required is low voltage AC. So I think that the starting point is to hear that side of the issue before listening to sales pitches about the benefits of special waveforms.

"Electrolytic Coloring of Anodized Aluminum Using Tin Electrolytes" by Gohausen & Schoener (Plating & Surface Finishing, Feb. 84) is a great intro to the topic. Best of luck.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


2000

Q. I was reading your response above and I'm interested in know more about electro coloring anodizing, at this time I'm coloring with Tin solution, but I have doubts about output voltages, I have an 3000 amp 30 volts AC coloring power supply by Dynapower, with five steps:

1.-dwell time
2.-pretreatment
3.-stage # 1
4.-stage # 2
5.-add

Where can I get "Electrolytic Coloring of Anodized Aluminum Using Tin Electrolytes" by Gohausen & Schoener (Plating & Surface Finishing, Feb. 84) ?

Or a newest ?

Marco Lopez
- Guadalajara, Jalisco, Mexico


2000

A. You may be able to get a copy from the publisher of Plating & Surface Finishing, the A.E.S.F. Contact their publications department at www.nasf.org

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



TUTORIAL FOR NEWBIES:
Yasar and Harmanto seem be speaking of true BLACK coloring. But readers should know that the dark gray to charcoal color they see on hard anodized pans is not dye of any sort at all -- it's just the natural consequence of hard anodizing (thick anodizing) on aluminum alloys which contain other metals which discolor it.

2003

Q. Could Tin sulfate be used for coloring (black) aluminum utensils (AA3003 alloy) in hard anodizing process? If yes, is it harmful for health.

Yasar Bayraktar
- Seydisehir, Konya, Turkey


2003

A. Salam:
tin sulfate is a green chemical, not harmful. But blackening with that is not an easy technique.
It's better to trial first according to additional chemical, concentration, timing and current density used.

harmanto soebawi
- bangka island, indonesia



Anolok Finish for Aluminum Extrusions?

2004

Q. I am into selling Aluminum Extrusions for architectural projects. I would like to know the process how to color an aluminum extrusion, preferably from a mill-finished aluminum extrusion into an Anolok (color) finish.

Thank you.

Allan Javier
Aluminum Extrusions Trading - Pasig, Metro Manila, Philippines


2004

A. That process involves first anodizing the parts and then transferring immediately to a plating tank containing usually tin or nickel salts. A.C. is passed to the parts by ramping up the current slowly and usually bronze or black colors are obtained.

Leeleongtee [last name deleted for privacy by Editor]
- Malacca, Malaysia


A. Thanks Leeleongtee.
Hi Allan. Leeleongtee's answer is right is one sense but incorrect in another sense :-) You can get a UV-stable inorganic black color (similar in color to Anolok) through the method which he describes. However, that is not how Anolok obtains the color in their process.

Luck & Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



May 23, 2009

DEAR SIR,

WE HAVE PLATED BLACK ANODISED COMPONENTS. WHEN CUSTOMER USES THIS COMPONENTS EXPOSED TO SUNLIGHT COLOUR OF EXPOSED TO SUNLIGHT FADES TO BROWNISH AND SOME COMPONENTS COLOUR TOTALLY FADES. CAN YOU THROW SOME LIGHT ON IT.

THANKS,

KAMLESH BHATT
PLATING MANAGER - PUNE, MAHARASTRA, INDIA


May 25, 2009

? Hi, Kamlesh. What does the vendor of the dye rate the lightfastness at?

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


simultaneous May 26, 2009

A. SEALING is required. While the fastness of the dye is of concern, there aren't that many dyes available to our industry that are that poor that they fade within weeks UNLESS the sealing is bad or altogether skipped. Sealing is the final process used in anodizing following the dye step to swell the tops of the aluminum oxide pores shut by hydrating the Al2O3 with 6 waters of hydration Al2O3.6H2O. This swelling locks in the dye and retains the colorfastness (and heat and chemical fastness).

milt stevenson jr.
Milt Stevenson, Jr.
Anoplate Corporation
supporting advertiser 
Syracuse, New York
Anoplate banner


May 27, 2009

A. Other possibilities are the coating is too thin, or poor seal. Both of these can cause premature fading in sunlight.

Marc Green
Marc Green
anodizer - Boise, Idaho


May 27, 2009

A. It sounds like it may be a poor or non-existent seal. Double check that your seal is operating properly, and administer a few of the standard seal quality tests (one of the easiest rule of thumb measurements for black is to mix up a little 30% nitric and either dip the part in it or brush it on the part - depending on size. If the part looses a significant amount of color in a minute or two, your seal is bad).

Although hardcoat anodize is typically not sealed, anything dyed MUST be, or you'll see fading exactly as you've described.

Good luck!

Jim Gorsich
Accurate Anodizing Inc.
supporting advertiser
Compton, California, USA
accurate anodizing banner


June 9, 2009

A. Any organic dyes do not have good lightfastness, when in outdoor application the colour fades because UV in sunlight, the black colour is most sensitive to this, lightfastness is better with electrolytic coloring usually using tin, nickel or cobalt salt; It is possible to use a electrolytic coloring first and a organic dying in sequence;
The fade-O-meter method (a modification on the weathering test without water in the cycle) is used to evaluate the lightfastness of the anodic colored coating with a high-intensity ultraviolet mercury-arc lamp.

Franz Robert Wagner
- Blumenau, Santa Catarina, Brazil


June 18, 2009

Q. DEAR SIR,

WE ARE DOING ANODISING BLACK AND AFTER 48 HRS IN ULTRAVIOLET RAYS EXPOSED TO SUN COLOUR GOES AWAY.SO IS THERE ANY TEST TO CHECK WHETHER DYE OR SEALANT IS PERFECT. HOW MANY HRS OF ULTRAVIOLET TEST PERIOD.WHAT IS COST OF UNIT. IF WE WILL GO FOR COLOUR DYE OTHER THAN BLACK SAME PROBLEM DO WE FACE OR IT IS THE CASE WITH BLACK DYE ONLY. PL. GUIDE FOR THE SAME.

THANKS,

K.M.BHATT.

KAMLESH BHATT [returning]
PLATING MANAGER - PUNE, MAHARASTRA, INDIA


February 25, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. What is Anolok finish?? Is that the same as Natural Anodized or powder coated?

Foong YL
Design - Malaysia, KL


February 27, 2012

A. Hi, Foong.

It's often desirable for anodized coatings to have color rather than being Natural Anodized to aluminum color. While simple organic dyes are often used in anodizing, these are usually not considered robust enough for architectural work. In that case, colors are applied via metallic salts; Anolok is a proprietary name for a licensed way of doing this; "two-step electrolytic coloring" with these salts, and described by Leeleongtee is another way.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


February 24, 2017

A. Anolok is an anodised finish primarily used in architectural applications, and a registered trademark of United Anodisers in the UK.

peter watts
United Anodisers - huddersfield england



2006

Q. I purchase an anodizing service loosely described as "two step" in my specifications, which also refer to tin sulfate in the process. The anodizer who currently provides this service tells me that the tin sulfate is the second step and provides the black finish my parts have after processing (the first step is merely a clear anodize). I am not familiar with this process and would like to know if:
a)it is commonly known by another name,
b)if it's a relatively common process that can be found globally (my primary machining supplier is in Singapore and I would like to see if he can provide parts complete) and
c)if the minimum lot charge of nearly double what I pay for my other anodizing jobs is justified. Thanks in advance for any assistance that might be provided.

Fred Tafel
- Mentor, Ohio, USA


affil. link
"Surface Treatment & Finishing of Aluminium and Its Alloys"
by Wernick, Pinner & Sheasby
from Abe Books
or
info on Amazon

affil. link
probert book
Aluminum How-To

"The Chromating - Anodizing - Hardcoating Handbook"
by Robert Probert
$89

2006

A. Anodizing without subsequent dying produces "clear" aluminum colored parts, Fred, assuming the aluminum is quite pure. If the alloy is rich in copper or silicon, even clear anodizing will come out gray to charcoal.

Anodized parts can be dyed with organic dyes (rather similar to clothes dye but optimized for aluminum), but such colors are not completely lightfast . . . sometimes not very lightfast at all. For greater lightfastness, metal salts can be electrolytically deposited at the base of the anodizing pores, and this is called two-step anodizing. And yes, every anodizing shop should have at least a general understanding of the concept but most probably don't offer two-step anodizing.

Two-step anodizing involves this second electrolytic process and it may also involve a subsequent organic dye to get a fully saturated color as well. It is a premium process, and not all shops are set up to be able to do it, so it will be more expensive. It's hard to say from a distance whether "nearly double" is the right price, but it doesn't seem to be the manifestly wrong price.

Anodizers apply their decades of experience to get you a good finish, so don't make the mistake of thinking anybody can do it, and easily. That is not to assert that there are no shops in and around Singapore with the requisite experience, but it is to say that you shouldn't let a shop "try their hand" at it. You need to find a shop which already does two-step anodizing and you need to have sample parts that they produced in hand before making commitments. Good luck!

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



February 24, 2011

Q. We are designing a new production line to produce mirror image of nickel finish for aluminium profile . So far I have been unable to find out the chemical that needed for nickel finish and the way of doing it. We able to produce the mirror image by using three chemicals which are H3PO4, H2SO4 and HNO3. But we have difficulty in getting the nickel finish color (some sort like light champagne color). Seeking for expertise here.
Thanks in advance.

Jay Lee
process engineer - Klang, Selangor, Malaysia


February 25, 2011

A. Hi, Jay.

There should be plating and anodizing process suppliers or consultants in your area who can help you get started; you do not need to independently re-invent these technologies. It sounds like you are doing brite-dipping of aluminum. To my knowledge this process will not by itself produce any coloration. After that, I think you will need to anodize the sheet, dye it with a nickel or light champagne dye, and then seal it.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


February 25, 2011

Q. I agree with you that brite-dipping of aluminum will not produce any coloration. Our lines do have anodizing process. But I do not have any ideas on how to produce the nickel finish after anodizing process (We have no problem on the anodizing process).
What is the chemical solution that needed (nickel sulphate)? What is the concentration and the process parameter (eg. temperature, pH...). Is this process called nickel plating? Hope that someone can give me a hand on this.
Thanks..

Jay Lee [returning]
- Klang, Selangor, Malaysia


simultaneous February 28, 2011

Jay, if you are looking to give a champagne color (similar to ENP shade)to the anodized aluminum, you would have to electro color the articles in a tin sulphate solution for a few seconds. You would have to add the electro color bath to your anodizing line for this purpose.Please understand that the bath has to be regularly maintained to give consistent color. Color can also vary depending on the aluminum alloys.

Winston D'Souza
- Bombay, India


February 28, 2011

Jay,

Your second posting make things a lot clearer.The process you are looking for is not nickel plating. It is called electrolytic coloring, usually for architectural profiles. The beauty electrolytic coloring is that they don't fade when expose to to UV light ( sunlight ) as compared to organic dyes.

Electrolytic coloring deposits metal salts into the anodized pores, usually, salts of nickel,cobalt, tin etc., using AC voltage. Yes, nickel sulfate is one of the metal salts used. Instead of re-inventing the wheel, you'll be better off getting the coloring solutions from suppliers which comes along with tech support.

SK Cheah
- Penang, Malaysia



Tin sulphate concentration in electrolytic coloring bath jumps up & down

June 16, 2017

Q. Dear finishing team ,
I am a laboratory technical in aluminum extrusion company
I want to ask about coloring bath , it must be (17-19)g/l concentrated of SnSO4 ,and we reach this level of concentration but suddenly it dropped down to 13 and can't make it rise to 17 anymore , we added a lot of gallons to repair it but it still 13-14 g/l
after two months it repair it self and give us 17-19 g/l concentration without we do any thing to it !
Now a days we have this problem again , the concentration dropped to 14 g/l, we added 10 gallons which is 25kg for each gallon then the concentration rise to 16
next day we add 6 gallons and it still 16 ! we added another 6 gallons in the next day and it still 16 !
I hope to find justification for this and what should we do !
Best regards,

Eng. abeer abuzaid
engineer - Amman, Jordan



Why does electrolytic coloring use AC current?

June 19, 2017

Q. I have a question about electrolytic coloring on anodized aluminium. Why this process use AC to deposit color? In my understand I think this technique like a electrolytic deposition technique that use DC to do. And I would like to tell you that I very new in this field especially about electric so I would like to apologize you if my question is like a stupid question. And the second is if I do some experiment what is the criteria to choose AC or DC to do? Because I'm very confuse about that like a electrolytic coloring technique that I mention above.

Thank you everyone to suggest me ^^.

Nattapon Pornnumpa
- Bangkok. Thailand



Chalking after electrocolor dying process on anodized aluminum

August 28, 2019

Q. Good am sirs,
we have a problem about our aluminum finished product, the surface becomes powdery after our electrocoloring process and it has an effect on the color appearance of the aluminum, I hope you can help me -- we are using a tin bath and the temp. of the solution ranges from 20-25 °C, std stannous concentration is 5-15 g/L actual: 7g/L
Nickel Sulphate: 26 g/L

Thank you in advance!

dhazel de mesa
- philippines



December 24, 2019

Q. Hello.
What is your opinion for black colour for anodizing aluminum in the electrocolouring bath?

What is the advantage and disadvantage?

mary alaii
aldoran - mosel.iraq



Bleed out problem with black anodize on a tin sulfate electro color process

March 19, 2020

Q. Hi! I'm a chemical engineer in charge of an anodizing plant of aluminum profiles for architectural purposes (6061).
We are having an issue with our darker finishings like dark bronze and black. The color "bleed out" after the cold sealing. We tested removing one profile of the rack before the submersion in the sealing bath. The difference is overwhelming.

43248-1

We decided to change the sealing bath, cause we knew it was contaminated with Al, but after that there were no improvements.
After an analysis we can not ensure if the problem is the sealing or a bad deposition of tin into the pores.
Process info:
Anodize: 150g/L sulphuric, 20-21 °C, <10 g/L Al, 15 microns.
Electrocolor: 9,5 g/L tin sulfate product, 20 g/L sulphuric.
Sealing: Nickel base product.

I hope someone had dealt with some similar problem.
Thanks!

Enzo F. Castro
- Corrientes, Argentina



October 22, 2020 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi everyone, can someone give me information about Inorganic Black Coloring of aluminum alloys,

RFQ: ... and also some companies that process it.
Thank you.

Paolo Stenta
- Forlì Italy
  ^- Privately contact this inquirer -^


October 2020

A. Hi Paolo. We appended your inquiry to a thread which explains it. For most applications, aluminum is dyed with organic dyes, but they can be subject to UV bleaching and other causes of fading. Inorganic or metallic dyeing is done via integral color anodizing or, probably more commonly these days, two-step electrolytic anodizing which deposits a tin, nickel, or other metal in the anodizing pores.

We no longer offer public suggestions of brands or sources for a number of time-proven reasons (why?), but potential vendors can contact you privately.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


October 24, 2020

A. Paolo

The European Cooperation for Space Standardization has an interesting document that may get you started:
"Black-anodizing of metals with inorganic dyes, ECSS-Q-ST-70-03C"

Willie Alexander
- Green Mountain Falls, Colorado

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